A Novel X-Linked Variant c.1772delG (p.G591fs*20) in IRS4 in Two Related Patients with Central Hypothyroidism

Central hypothyroidism (CeH) is characterized by thyroid hormone deficiency due to impairment of pituitary thyroid stimulating hormone or hypothalamic TRH biosynthesis. It is extremely rare and affects approximately 1:16,000-100,000 individuals. Diagnosis, especially of isolated CeH, may be challenging. CeH is often seen as a part of multiple pituitary hormone deficiencies, but it can also be seen as isolated CeH. To date, some variants that can cause CeH have been identified, although in a number of patients the cause has not been clarified. Recently, variants of the insulin receptor substrate 4 (IRS4) gene have been reported to be the cause of isolated CeH. Herein, we report two related patients and their family with carriers with a novel X-linked frameshift variant in the IRS4 gene. It has also been shown that thyroid function may be slightly affected in the heterozygous female carriers in our study.

Herein, we reported two Turkish male patients with CeH due to a hemizygous variant in IRS4. The index case was a 15-year-and-2-month-old male who presented with a low serum-free thyroxin level, which was incidentally detected.

Isolated CeH should keep in mind in insistent low fT4 levels without an increase in thyroid stimulating hormone levels. Genetic testing can aid in identifying the underlying cause of CeH in such cases. This report demonstrates the significance of providing comprehensive laboratory and molecular features of the patients and carriers with the IRS4 variants.